What is Blender's maximum render size?
I don't think it is locked to 22000. I have personally rendered image 43000 + pixels in one dimension.

Biggest picture i rendered was around 30000x10000. All those was in multi layer EXR and .png

The bigger problem i found is saving those images. Blender crashed on me when i saved images this large. I have to render it in parts and compose whole image after.